This invention relates in general to analog signal processing, and in particular to an analog circuit for decomposing an input signal into analog wavelet outputs.
Analysis of an input signal in terms of frequency and time was first suggested in D. Gabor, Theory of Communication. Gabor realized that the informational content of some signals such as speech signals depends on time variations as well as frequency variations.
About ten years ago, based on Gabor's work, French scientists studied the decomposition of a signal into components with respect to frequency and time. They devised an orthogonal decomposition where values are placed in a "box" such that these values are unrelated to one another. This decomposition is called the "wavelet transform". As opposed to the Fourier transform which is dependent on frequency, the wavelet transform is dependent on both frequency and time.
Wavelet transforms have been suggested for use in data compression. The wavelet transform arranges the signal information in a manner that will facilitate data compression. For this reason, the use of wavelet transforms will be desirable in projected new consumer electronics products, such as digital telephone answering machines, that require data compression.
Lawton, U.S. Pat. No. 4,974,187, describes a system that decomposes a digital input sequence into its digital wavelet transform. The disadvantages of a digital wavelet transform circuit such as the one used in Lawton is that a digital wavelet transform circuit is large and uses a lot of power. Additionally, the digital sampling of an analog input to form the digital input sequence loses some of the information of the input signal. It is therefore desirable to provide an improved wavelet transform chip in which the above-described difficulties are not present.